A long time ago I had a friend who had a friend off-Island who had a dog who had a problem. I don’t remember the details. I just remember my friend’s friend sent my friend the medical records and asked my opinion. The dog was about 5 years old, a Great Dane mix. Let’s call him Bear. For several months Bear had been having vague signs that came and went. Some days he was lethargic. Other days he seemed fine. Some days he vomited or had diarrhea. Other days not. Over time, Bear got gradually thinner and seemed increasingly unwell. His veterinarian had done blood tests, taken radiographs, tried different treatments for all kinds of gastrointestinal diseases, but Bear did not improve.
I scanned Bear’s laboratory results quickly. Everything looked normal. No. Wait. Bear’s sodium levels were within the “normal range,” but at the very lower limit of what is considered normal. His potassium levels were also within “normal range,” but at the upper limit of what is considered normal. I took the sodium level (Na) and divided it by the potassium level (K) to get the “Na/K ratio.” We like to see that number be at least 27. Bear’s was 25. “I think he might have Addison’s disease,” I told my friend.
Also known as hypoadrenocorticism, Addison’s disease occurs when there is a malfunction of the adrenal glands, two tiny organs that sit right by the kidneys. These glands produce hormones including corticosteroids and mineralocorticoids. Corticosteroids help maintain homeostasis and normal metabolism. Insufficient corticosteroids can cause weight loss, anorexia, vomiting, and an inability of the body to respond properly to stress. Mineralocorticoids are responsible for maintaining proper balance of the electrolytes sodium and potassium, which in turn are essential for proper neurologic and muscle function. Too little sodium results in low blood pressure, kidney dysfunction, dehydration, and weakness. Too much potassium can stop the heart. Most cases of hypoadrenocorticism are immune-mediated, i.e., for some unknown reason, the body’s immune system attacks its own adrenal glands. It is most commonly seen in youngish female dogs, but any dog can be affected. Clinical signs may include lethargy, general malaise, vomiting, and diarrhea. It can be confusing to both owner and veterinarian, as symptoms tend to wax and wane.
Standard poodles, Great Danes, Rottweilers, and Portuguese water dogs have a higher incidence, but the first case I ever saw was a Dalmatian … and I missed the diagnosis. This sweet dog had been vomiting off and on for months. We finally decided to do an exploratory laparotomy. This means we went in surgically to try to determine the cause. Expecting to find a tumor, or inflammatory bowel disease, I checked every inch of her gut. I took biopsies. Everything was normal. It’s a terrible feeling, doing surgery and still not making a diagnosis. No one ever wants to put an animal through unnecessary procedures, but exploratory surgeries are often helpful. Not this time. We ultimately referred that Dalmatian to specialists, who diagnosed her Addison’s disease. I vowed never to miss this disease again.
I’m not the first veterinarian to get fooled. Hypoadrenocorticism is called the Great Imitator because it can look like so many other diseases. Diagnosis is tricky. Not every Addisonian dog has a consistently abnormal Na/K ratio. Often the diagnosis is not made until the dog experiences an “Addisonian crisis.” At this point, the lack of adrenal hormones throws the entire body into shock. The dog may have hypoglycemia and seizures. Electrolyte imbalances lead to life-threatening slowing of the heart and, left untreated, cardiac arrhythmias and death. Sounds like it would be simple to recognize, but in reality an Addisonian crisis can look exactly like many other medical crises.
Definitive diagnosis requires an ACTH stimulation test. I’ll spare you the details. Suffice it to say it evaluates the adrenal glands’ response to intravenous injection of a specific hormone. If we make the diagnosis before a dog goes into crisis, treatment involves replacing the missing hormones, either orally or by long-acting injections. Once an animal collapses, however, treatment requires hospitalization and aggressive therapy. Not all dogs survive. Whether crisis or chronic, it takes a while for everything to stabilize. Frequent monitoring is necessary, and treatment is lifelong
Just this week I saw Ursa, a middle-aged golden retriever, with a vague history of malaise. We call this ADR: Ain’t Doin’ Right. We ran blood work as a general screen. I wasn’t expecting Addison’s disease. Too old. Wrong breed. But there it was. Individually sodium and potassium were in the “normal” ranges, but the Na/K ratio was a hair low, at 26. Still, I didn’t think it was hypoadrenocorticism … but I couldn’t be sure, and had promised myself never to miss this diagnosis again.
Other things can throw off the electrolyte ratio. Certain breeds, like Akitas, normally run high potassium levels. The intestinal parasite whipworm can cause elevated potassium. But Ursa was a golden retriever, and we had ruled out whipworm. I suggested a simple test called a resting cortisol level. If resting cortisol is high enough, you can pretty much rule out Addison’s. Unfortunately, this is one of those tests that can rule something OUT, but cannot rule something IN. In other words, low resting cortisol isn’t proof of hypoadrenocorticism. For that you always need an ACTH stimulation test. When Ursa’s resting cortisol test came back slightly low, we ran an ACTH stimulation test to get a definitive answer.
I had been right about Bear all those years ago. The Great Dane mix did have Addison’s disease. He responded well to treatment, and went on to live happily on a farm somewhere. I missed it on the Dalmatian, but subsequently got it right on many dogs. What about Ursa? Her ACTH stimulation test was normal. This time it was not the Great Pretender. That’s great news! Now I just have to figure out why she ain’t doin’ right, and what we can do to help her feel better.